Elderly patients hospitalized with an infection, like pneumonia, are twice as likely to be diagnosed with dementia than those who were not.

That’s according to a new study from the University of Pittsburgh that followed 5,888 patients over the age of 65 in four areas across the country: Winston-Salem, N.C.; Sacramento, Calif.; Hagerstown, Md.; and Pittsburgh.

The study was done in conjunction with researchers from the University of Washington, University of California, University of Illinois, John Hopkins University and Columbia Medical Center.

Dr. Sachen Yende, senior author of the study and associate professor at Pitt, said doctors were hearing from families that their elderly loved ones would come down with pneumonia and never be the same mentally.

Dementia is difficulty with thinking and memory in patients severe enough to impact daily life; most of the cases of in the study were Alzheimer's dementia.

Yende said they also found that, once patients developed dementia, they had a greater risk of developing future infections.

“One can think about it as a vicious cycle where one event precipitates the other event and the next event then puts you at risk for the first event and leads to sort of a downhill progression,” he said.

Yende said pneumonia doesn’t necessarily cause dementia, but simply accelerates it. He believes most of the study’s subjects had dementia before contracting pneumonia, but the episode accelerated it and led to early presentation.

He said there are two messages that people can take away from the research, the first being that infections aren’t always “short-lived.”

“A single episode of infection could have a lot of downstream consequences that we don’t usually think of,” Yende said. “And I think that this is important to keep in mind as we come up to the flu season.”

Yende said the second message is for the medical community: do more research on infection and dementia so they can discover more ways to prevent both.

He said his team is now looking at how inflammation affects patients’ recovery from infection and whether it is connected to dementia.